Method for producing nodular cast iron

ABSTRACT

A method for producing nodular cast iron by using a nodulizer and a spheroidizing device, the method including spheroidizing, the spheroidizing including the following steps: a) placing an integrated rare earth magnesium ferrosilicon nodulizer coated with a rectangular steel tube at a preset position inside a spheroidizing ladle, disposing a strut head on the spheroidizing ladle, and fixing the strut head; b) inputting a ferrosilicon inoculant into the spheroidizing ladle; c) inputting melted iron into the spheroidizing ladle for spheroidizing; and d) removing the strut head from the spheroidizing ladle after spheroidizing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of International Patent Application No. PCT/CN2011/001762 with an international filing date of Oct. 24, 2011, designating the United States, now pending, and further claims priority benefits to Chinese Patent Application No. 201010517484.9 filed Oct. 25, 2010. The contents of all of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference. Inquiries from the public to applicants or assignees concerning this document or the related applications should be directed to: Matthias Scholl P. C., Attn.: Dr. Matthias Scholl Esq., 14781 Memorial Drive, Suite 1319, Houston, Tex. 77079.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for producing a nodulizer and a spheroidizing device, and more particularly to a spheroidizing method for producing nodular cast iron by using a nodulizer and a spheroidizing device.

2. Description of the Related Art

Rare earth magnesium ferrosilicon alloy has been widely used as a nodulizer in practical production for manufacturing nodular cast iron parts. The rare earth magnesium ferrosilicon nodulizer has the largest demand in all kinds of nodulizer in the world. However, a conventional production method thereof necessitates a high energy consumption, large melt loss, and serious environmental pollution; besides, a large amount of the conventional nodulizer is required because of a low absorption rate of magnesium. A pouring method of spheroidizing technology and the method for producing the rare earth magnesium ferrosilicon alloy have been study focuses for the researchers in the field for a long term.

The pouring method of spheroidizing technology by using the rare earth magnesium ferrosilicon nodulizer has problems that when the iron is at a temperature of exceeding 1480° C., a spheroidizing ladle is in a state of continuously used a hot glowing ladle, and when a content of magnesium is ≧8%, the spheroidizing becomes violent with the increase of the temperature, an intensive magnesium light occurs, or even iron melt splashes, which results in a low absorption rate of effective elements of magnesium and Re, a recession of the iron melt in a later period of the spheroidizing, and a decline of the spheroidizing level.

A typical solution is that 1) in smelting of the nodulizer, adding a certain amount of SiCa alloy for improving Ca content to alleviate the eruption, however, the addition of SiCa also increases the production cost; 2) controlling the content of magnesium in the nodulizer around 8% or within 8% to alleviate the reaction; 3) inputting rare earth magnesium ferrosilicon nodulizer inside a dam of the iron melt ladle, covering raw iron dust on the nodulizer and hitting the covering to be compact, or further inputting broken iron sheets to lower the temperature of the iron melt; 4) inputting the nodulizer and the ferrosilicon inoculant into the ladle and covering a perlite slag conglomeration agent or an iron sheet. Although the above solutions have good effects in controlling the violent reaction of the magnesium alloy, the iron melt has a large temperature difference before and after the spheroidizing, a large amount of dross floats on a surface of the iron melt, the stability of the spheroidizing varies according to the temperature of the iron melt, and the adsorption rates of effective elements of magnesium, Re, and silicon have large fluctuation ranges. For spheroidizing in a cupola furnace, if the original iron melt has a high sulfur content, it requires a larger amount of the nodulizer and a increase of the content of Re and calcium in the nodulizer. However, it is very difficult to increase the content of magnesium in the nodulizer in condition of high temperature treatment.

Conventional methods for producing a nodulizer include the following problems: to conduct spheroidizing in a spheroidizing device, a dam type spheroidizing ladle is required. The dam is required to be high enough in order to accommodate all the rare earth magnesium ferrosilicon nodulizer and the inoculant. For example, a dam height of a newly made spheroidizing ladle having a weight of 1000 kg is required to be 23 cm. The increase of the dam height results in a height increase of flashpoint of the nodulizer during the melting boiling reaction thereof, which is not conducive to adsorption of effective elements and cleaning of the iron melt. A position of the strut head is regulated according to the condition of the spheroidizing in order to control the reaction time of the spheroidizing, a relatively long reaction time is needed to prevent magnesium light and smoke. Furthermore, the dam in the spheroidizing ladle is prone to stick dross and to be damaged, which affects the quality of the whole spheroidizing, and increases the labor in repairing the iron melt ladle.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is one objective of the invention to provide a method for producing nodular cast iron by using a nodulizer and a spheroidizing device that effectively solves problems of violent spheroidizing reaction and low adsorption rate of effective elements. The method is capable of accurately controlling the reaction time of the spheroidizing, improving the product quality, lowering the production cost, effectively using the resource, and obviously improving the manufacturing process of the nodulizer and the environment of the spheroidizing.

To achieve the above objective, in accordance with one embodiment of the invention, there is provided a method for producing nodular cast iron by using a nodulizer and a spheroidizing device. The nodulizer is prepared by providing a rectangular or square steel tube comprising a pressure regulating through hole or a pressure regulating gap arranged on a middle part of a side surface thereof. For the rectangular steel tube, the pressure regulating through hole is arranged on a middle part of an end surface of a relatively small area; injecting an alloy melt of rare earth magnesium ferrosilicon nodulizer comprising magnesium ≦20%, silicon ≦65%, and Re ≦3% from the pressure regulating through hole or the pressure regulating gap into the rectangular or square steel tube to condense and cool, thereby obtaining a nodulizer block coated with the rectangular or square steel tube with two opening ends; and using a steel plate having a same thickness as a wall of the rectangular or square steel tube to close a part of an opening of each of the two ends of the rectangular or square steel tube by means of welding for reducing a contact area between a high temperature iron melt and the nodulizer block and for controlling a reaction time and reaction state of the nodulizer. The spheroidizing device taught by Chinese patent publication number CN101029367A titled as a spheroidizing device and a method by using the same is adopted. The spheroidizing device comprises: a strut head (1), a steering shaft (2), a mobile location (3), a pressure lever (4), a balance steel (5), a column and a positioning ruler (6), a first bolt (8), and a third bolt and a nut thereof (12). The strut head (1) is movable and fixable at a required position. A bottom surface of the strut head (1) is flat. A fire-proof material coated on the strut head (1) is a frame welded by threaded steel and an iron wire. The strut head (1) is capable of tolerating repeated hits from the high temperature iron melt and from the nodulizer having a magnesium content ≦20% during an intensive melting and boiling reaction thereof. The column and the positioning ruler (6) are welded as a whole body. The mobile location (3) is arranged on an end part of the positioning ruler. The balance steel (5) is hanged on the other end of the pressure lever (4). The nodulizer coated with the rectangular or square steel tube (13) is a compact cuboid that has a relatively small volume. An integrated rare earth magnesium ferrosilicon nodulizer (14) has a relatively low height of a flashpoint in the melting and boiling reaction, and the spheroidizing occurs in a horizontal direction, which is conducive to the adsorption of the effective element and the cleaning of the iron melt.

The spheroidizing ladle is a flat bottom spheroidizing ladle or a dam type spheroidizing ladle comprising a relatively short dam. For the flat bottom spheroidizing ladle, as shown in FIGS. 1-3, place an integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube into the spheroidizing ladle to assure the surface comprising the pressure regulating through hole (17) close to a middle part of the spheroidizing ladle; dispose and fix the strut head (1) on the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube; and input a ferrosilicon inoculant into the spheroidizing ladle close to a ladle wall. For dam type spheroidizing ladle comprising the short dam, as shown in FIGS. 4-5, place an integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube into the spheroidizing ladle to assure that the surface comprising the pressure regulating through hole (17) is close to the ladle wall and an opposite surface is attached to the dam; dispose and fix the strut head (1) on the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube; and input the ferrosilicon inoculant into the spheroidizing ladle close to the two openings and the ladle wall. In conditions of no pressure regulating hole (17) or pressure regulating gap (19), the iron melt is poured into the spheroidizing ladle, the nodulizer at the two openings of the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube first becomes in contact with the high temperature iron melt, melts, and boils. The later reacted nodulizer, because the depth thereof become large and the pressure of boiling reaction increases, the frequency of the melting and boiling reaction of the nodulizer becomes lower, and the iron melt boils more intensively. As shown in FIGS. 3-6, in the presence of the pressure regulating hole (17) or pressure regulating gap (19), the melted and boiled nodulizer ejects from the pressure regulating hole (17) or pressure regulating gap (19), thereby shortening the distance of the melting and boiling reaction of the nodulizer, decreasing the pressure, and alleviating the reaction condition. It is experimentally found that, in condition that the coated rectangular or square steel tube (13) has a length larger than 25 cm and is provided with the pressure regulating through hole (17) having a diameter of 8-14 mm, the effect of the spheroidizing is desired. For the coated rectangular or square steel tube (13) having a length larger than 25 cm and provided with the pressure regulating gap (19), a width of the pressure regulating gap (19) is preferable 2-4 mm. When the iron melt has a relatively high temperature, reduce the area of the openings of the pressure regulating through hole (17) or the pressure regulating gap (19); and when the iron melt has a relatively low temperature, enlarge the area of the openings of the pressure regulating through hole (17) or the pressure regulating gap (19).

The strut head (1) is disposed and fixed on the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube by using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as an rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1); or the strut head (1) is disposed on the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube by using an electric motor to drive a lifting device, hanging the strut head (1) provided with a counterweight iron (15) on a hook of the lifting device: based on the means of using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as an rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1), the strut head (1) is provided with the counterweight iron (15), after the spheroidizing, the strut head (1) is removed from the spheroidizing ladle. A third means to dispose and fix the strut head (1) on the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube is as shown in FIG. 7, a positioning shaft sleeve (25) is welded on an upper end of an outer side of the spheroidizing ladle (7) and connected to the strut head (1); an end of a positioning handle (23) is provided with a thread, the thread matches with a nut welded on the positioning shaft sleeve (25); the thread of the end of the positioning handle (23) passes through the positioning shaft sleeve (25) and fastens the strut head (1); and a position of the strut head (1) in the spheroidizing ladle (7) is adjusted by the positioning handle (23); the strut head (1) is movable and fixable at the required position; the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube or by the square steel tube is fixed beneath the strut head (1); and the bottom surface of the strut head (1) is flat; the fire-proof material coated on the strut head (1) is a frame welded by a round steel, a steel bar, and the iron wire. As shown in FIG. 7, the positioning shaft sleeve (25) is connected to the strut head (1), during the spheroidizing of the poured iron melt, the strut head is movable along with the spheroidizing ladle.

To further improve the utilization of the rare earth elements, during the spheroidizing is conducted by using the above three means for placing and fixing the strut head (1), as shown in FIGS. 8-9, an integrated rare earth magnesium ferrosilicon alloy (21) having a content of rare earth ≦33% and coated with a rectangular or square steel tube is arranged inside an integrated magnesium ferrosilicon nodulizer (20). A direction of an opening of the integrated magnesium ferrosilicon nodulizer (20) coated with the rectangular or square steel tube is the same as a direction of an opening of the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube. The integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube is bound to a compositely coated rectangular or square steel tube (22) by welding. An alloy melt of the integrated magnesium ferrosilicon nodulizer (20) is injected into the compositely coated rectangular or square steel tube (22) to condense and cool. In order to accelerate the cooling of the alloy melt of nodulizer, the cooling iron is arranged between a combination of the rectangular or square steel tubes being filled with the alloy melt of the nodulizer for preventing component segregation of the nodulizer. The iron melt is input into the spheroidizing ladle (7) for spheroidizing. During a later half of the reaction time, the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube participates in the spheroidizing for supplying a required amount of rare earth.

Because the rectangular or square steel tube (13) has an uniform appearance, after placing the openings of the combination of the rectangular or square steel tube (13) upwards, the alloy melt of rare earth magnesium ferrosilicon nodulizer produced by a one step-method for smelting ferrosilicon alloy in a submerged arc furnace or by a remelting method in an electric furnace is poured into the rectangular or square steel tube (13). Because of the rectangular or square steel tube (13) and the cooling iron, the process of cooling and condensing of the alloy melt of the nodulizer is accelerated, and the component segregation of the nodulizer is eliminated. The integrated nodulizer alloy coated with the rectangular or square steel tube (13) is not required to be broken down and screened, thereby being convenient to move and stack.

The spheroidizing method comprising the following steps:

-   -   a) placing the integrated rare earth magnesium ferrosilicon         nodulizer (18) coated with the rectangular steel tube at a         preset position inside the spheroidizing ladle (7), disposing         the strut head (1) on the spheroidizing ladle (7), and fixing         the strut head (1);     -   b) inputting a ferrosilicon inoculant into the spheroidizing         ladle (7);     -   c) inputting melted iron into the spheroidizing ladle (7) for         spheroidizing; and     -   d) removing the strut head (1) from the spheroidizing ladle (7)         after the spheroidizing.

Advantages of the invention are summarized as follows:

The method effectively solves problems of violent spheroidizing reaction and low adsorption rate of effective elements. The method is capable of decreasing the temperature difference, realizing a non-magnesium light and non-smoke spheroidizing, and accurately controlling the reaction time of the spheroidizing. An error is controlled within 5 seconds when a temperature fluctuation of the iron melt is within 30° C.

Compared with a conventional nodulizer having 8% of magnesium, 5% of Re, and 41% of silicon, an integrated nodulizer having 15% of magnesium, 1% of Re, and 54% of silicon coated with rectangular or square steel tube (13) produced by herein, that is, compared with a conventional rare earth magnesium ferrosilicon nodulizer, the integrated rare earth magnesium ferrosilicon nodulizer coated with the rectangular or square steel tube produced by the one step method or the remelting method in the electric furnace, the production cost thereof is lowered by 20-30%, and a dosage of thereof is decreased by 25-30%.

It is experimentally found that the spheroidizing temperature of the method is between 1450-1578° C. The amount of the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube and the reaction time of the spheroidizing do not change, and the result of the spheroidizing is not affected, thereby overcoming problems that the required amount of the nodulizer increases in accordance with the increase of the spheroidizing temperature in conventional spheroidizing process.

After the spheroidizing, an additional nodulizer is supplied by means of using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as the rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1) or by means of using the electric motor to drive the lifting device, hanging the strut head (1) provided with the counterweight iron (15) on the hook of the lifting device, the additional integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube is bound to the bottom surface of the strut head (1) by an iron wire and an iron sheet, and is pressed down into the iron melt for supplying a required amount of magnesium. The method obviously improves the manufacturing process of nodulizer and the environment of the spheroidizing.

In conditions of the same chemical components of the rare magnesium ferrosilicon nodulizer and the same spheroidizing temperature, the spheroidizing by using the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular or square steel tube has a more accurate and shorter reaction time, higher adsorption rates of effective elements of magnesium, Re, and silicon. For the conventional rare earth magnesium ferrosilicon nodulizer having a Re content of 2-8%, the Re content is lowered by 50-75% by using the method of the invention. Additional magnesium can be added in time if necessary.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described hereinbelow with reference to the accompanying drawings, in which:

FIG. 1 is a cutaway view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a flat bottom spheroidizing ladle 7 by means of using a third bolt and a nut thereof 12 disposed on a column and a positioning ruler 6 as an rotational axis of the pressure lever 4, arranging a steering shaft 2 on the pressure lever 4, and connecting a first bolt 8 of the steering shaft 2 to a strut head 1;

FIG. 2 is a top view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a flat bottom spheroidizing ladle 7 and fixed beneath a strut head 1;

FIG. 3 is a cutaway view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a flat bottom spheroidizing ladle 7 and fixed beneath a strut head 1;

FIG. 4 is a top view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a dam type spheroidizing ladle 7 and fixed beneath a strut head 1;

FIG. 5 is a cutaway view an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a flat bottom spheroidizing ladle 7 by means of using an electric motor to drive a lifting device, hanging the strut head 1 provided with a counterweight iron 15 on a hook of the lifting device;

FIG. 6 is a cutaway view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube provided with a pressure regulating gap 19;

FIG. 7 is a cutaway view of an integrated rare earth magnesium ferrosilicon nodulizer 18 coated with a rectangular or square steel tube being placed inside a flat bottom spheroidizing ladle 7 by means of using a positioning shaft sleeve 25 welded on an upper end of an outer side of the ladle for connecting to a strut head 1;

FIG. 8 is a cutaway view of an integrated rare earth magnesium ferrosilicon alloy having a content of rare earth ≦33% and coated with a rectangular or square steel tube 21 being placed inside an integrated magnesium ferrosilicon nodulizer 20 of a compositely coated rectangular or square steel tube 22; and

FIG. 9 is a left view of an integrated rare earth magnesium ferrosilicon alloy having a content of rare earth ≦33% and coated with a rectangular or square steel tube 21 being placed inside an integrated magnesium ferrosilicon nodulizer 20 of a compositely coated rectangular or square steel tube 22.

In the drawings, the following reference numbers are used: 1. Strut head; 2. Steering shaft; 3. Mobile location; 4. Pressure lever; 5. Balance steel; 6. Column and a positioning ruler; 7. Spheroidizing ladle; 8. A first bolt; 9. A second bolt; 10. A first bolt and a nut thereof; 11. A second bolt and a nut thereof; 12. A third bolt and a nut thereof; 13. Coated rectangular or square steel tube; 14. Integrated rare earth magnesium ferrosilicon nodulizer; 15. Counterweight iron; 16. Hook of a lifting device; 17. Pressure regulating through hole; 18. Integrated rare earth magnesium ferrosilicon nodulizer coated with the rectangular or square steel tube; 19. Pressure regulating gap; 20. Integrated magnesium ferrosilicon nodulizer; 21. Integrated rare earth magnesium ferrosilicon alloy having a content of rare earth ≦33% and coated with a rectangular or square steel tube; 22. Compositely coated rectangular or square steel tube; 23. Positioning handle; 24. Nut welded on a positioning shaft sleeve; and 25. Positioning shaft sleeve.

DETAILED DESCRIPTION OF THE EMBODIMENTS

For further illustrating the invention, experiments detailing a method for producing nodular cast iron by using a nodulizer and a spheroidizing device are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

An integrated rare earth magnesium ferrosilicon nodulizer 14 is coated with a rectangular or square steel tube 13. The coated rectangular or square steel tube 13 is critical to control the reaction state and reaction time of the rare earth magnesium ferrosilicon alloy. When a dam type spheroidizing ladle is used for spheroidizing, because the coated rectangular or square steel tube 13 is compactly encircled by a fire-proof material of a ladle bottom, a bottom of the dam, and a bottom of the strut head 1, and another surface is covered by a ferrosilicon inoculants, the melting speed of the coated rectangular or square steel tube 13 is lowered. Thus, a thickness of a wall of the coated rectangular or square steel tube 13 is controlled between 2-4 mm; when the spheroidizing temperature is 1480° C., the reaction time is relatively long. When a flat bottom spheroidizing ladle is used, the thickness of the wall is an upper limit of the range, a surface of the openings of the rectangular or square steel tube 13 is coated with a fire-proof material to mollify the melting. Or the coated rectangular or square steel tube 13 is made of cast iron by casting.

It is found experimentally that to prevent that the spheroidizing period is too short and the reaction is too violent, the integrated rare earth magnesium ferrosilicon nodulizer 14 is placed into a spheroidizing ladle that has a height of less than 12 cm; when the height of the ladle is larger than 12 cm, the structure of rectangular steel tube is adopted, and a size of a relatively small surface of the rectangular steel tube is less than or equal to 12 cm. A steel plate having a same thickness as the wall of the rectangular steel tube is used to close a part of an opening of each of two ends of the rectangular steel tube; the coated rectangular or square steel tube 13 and the steel plate are made of carbon steel and have no coating.

Example 1

In a melting condition by using a cold copula furnace, a melting rate is 2 tons per hour, the integrated rare earth magnesium ferrosilicon nodulizer 18 coated with the rectangular steel tube is placed inside the dam type spheroidizing ladle 7 by means of using the third bolt and the nut thereof 12 disposed on the column and the positioning ruler 6 as an rotational axis of the pressure lever 4, arranging the steering shaft 2 on the pressure lever 4, and connecting the first bolt 8 of the steering shaft 2 to the strut head 1, as shown in FIG. 1. A weight of the iron melt to be treated in each ladle is 500 kg, a hot glowing ladle continuously operates, and a temperature of the iron melt of the iron notch is 1480° C. A sulfur content of an original iron melt is 0.062%. An integrated rare earth magnesium ferrosilicon nodulizer 14 not including the coated rectangular steel tube contains 16% of magnesium, 2% of Re, and 54% of silicon. The weight of the integrated rare earth magnesium ferrosilicon nodulizer 18 coated with the rectangular steel tube is 1.2% of the weight of the treated iron melt. An amount of a 72SiFe inoculant is 0.4%, and an amount of a secondary silicon barium inoculant is 0.15%. In conditions of no covering of the iron dust and perlite, the time of the spheroidizing is 80 seconds, no magnesium light occurs during iron melt boiling reaction. Samples are collected 8 minutes and 30 seconds after the spheroidizing, and the spheroidizing level is two.

Example 2

In a melting condition by using an intermediate frequency electric furnace, the integrated rare earth magnesium ferrosilicon nodulizer 18 coated with the rectangular steel tube is placed inside the flat bottom spheroidizing ladle 7 by using the third bolt and the nut thereof 12 disposed on the column and the positioning ruler 6 as an rotational axis of the pressure lever 4, arranging the steering shaft 2 on the pressure lever 4, and connecting the first bolt 8 of the steering shaft 2 to the strut head 1, as shown in FIG. 3. A weight of the iron melt to be treated in each ladle is 1000 kg. A temperature of the iron melt of the iron notch is 1578° C. A sulfur content of an original iron melt is 0.028%. An integrated rare earth magnesium ferrosilicon nodulizer 14 contains 15% of magnesium, 1% of Re, and 54% of silicon. The weight of the integrated rare earth magnesium ferrosilicon nodulizer 18 coated with the rectangular steel tube is 0.8% of the weight of the treated iron melt. An amount of a 72SiFe inoculant is 0.4%, and an amount of a secondary silicon barium inoculant is 0.2%. In conditions of no covering of the iron dust and perlite, the time of the spheroidizing is 1 minute and 56 seconds. The spheroidizing is table, and no iron splash occurs. Samples are collected 12 minutes after the spheroidizing, and the spheroidizing level is two.

While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention. 

The invention claimed is:
 1. A method for producing nodular cast iron by using a nodulizer and a spheroidizing device; the nodulizer being prepared by providing a rectangular steel tube (13) comprising a pressure regulating through hole (17) arranged on a middle part of a side surface thereof; for the rectangular steel tube, the pressure regulating through hole (17) being arranged on a middle part of an end surface of a relatively small area; injecting an alloy melt of a rare earth magnesium ferrosilicon nodulizer comprising magnesium ≦20%, silicon ≦65%, and Re ≦3% from the pressure regulating through hole (17) into the rectangular steel tube (13) to condense and cool; a diameter of the pressure regulating through hole (17) being 8-14 mm; using a steel plate having a same thickness as a wall of the rectangular steel tube to close a part of an opening of each of two ends of the rectangular steel tube by means of welding for controlling a reaction time and reaction state of the nodulizer; the spheroidizing device comprising: a strut head (1), a steering shaft (2), a mobile location (3), a pressure lever (4), a balance steel (5), a column and a positioning ruler (6), a first bolt (8), and a third bolt and a nut thereof (12); the strut head (1) being movable and fixable at a required position by using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as an rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1); a bottom surface of the strut head (1) being flat; a fire-proof material coated on the strut head (1) being a frame welded by a threaded steel and an iron wire; the column and the positioning ruler (6) being welded as a whole body; the mobile location (3) being arranged on an end part of the positioning ruler; the balance steel (5) being hanged on the other end of the pressure lever (4); the method comprising spheroidizing, and the spheroidizing comprising the following steps: a) placing an integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube at a preset position inside a spheroidizing ladle (7), disposing the strut head (1) on the spheroidizing ladle (7), and fixing the strut head (1); b) inputting a ferrosilicon inoculant into the spheroidizing ladle (7); c) inputting melted iron into the spheroidizing ladle (7) for spheroidizing; and d) removing the strut head (1) from the spheroidizing ladle (7) after the spheroidizing.
 2. The method of claim 1, wherein the rectangular steel tube (3) is a square steel tube.
 3. The method of claim 1, wherein the alloy melt of the rare earth magnesium ferrosilicon nodulizer is poured into the rectangular steel tube (13); and the alloy melt is produced by a one-step method for smelting ferrosilicon alloy in a submerged arc furnace or by a remelting method in an electric furnace.
 4. The method of claim 2, wherein the alloy melt of the rare earth magnesium ferrosilicon nodulizer is poured into the square steel tube (13); and the alloy melt is produced by a one-step method for smelting ferrosilicon alloy in a submerged arc furnace or by a remelting method in an electric furnace.
 5. The method of claim 1, wherein cooling iron is arranged between a combination of the rectangular or square steel tubes being filled with the alloy melt of the nodulizer.
 6. The method of claim 2, wherein cooling iron is arranged between a combination of the rectangular or square steel tubes being filled with the alloy melt of the nodulizer.
 7. The method of claim 1, wherein the spheroidizing is processed by using an electric motor to drive a lifting device, hanging the strut head (1) provided with a counterweight iron (15) on a hook of the lifting device to substitute the means of using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as the rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1).
 8. The method of claim 2, wherein after the spheroidizing, an additional nodulizer is supplied by means of using the third bolt and the nut thereof (12) disposed on the column and the positioning ruler (6) as the rotational axis of the pressure lever (4), arranging the steering shaft (2) on the pressure lever (4), and connecting the first bolt (8) of the steering shaft (2) to the strut head (1), the additional integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube is bound to the bottom surface of the strut head (1) by an iron wire and an iron sheet, and is pressed down into the iron melt for supplying a required amount of magnesium.
 9. The method of claim 7, wherein after the spheroidizing, an additional nodulizer is supplied by means of using the electric motor to drive the lifting device, hanging the strut head (1) provided with the counterweight iron (15) on the hook of the lifting device, the additional integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube is bound to the bottom surface of the strut head (1) by an iron wire and an iron sheet, and is pressed down into the iron melt for supplying a required amount of effective magnesium element.
 10. The method of claim 1, wherein a positioning shaft sleeve (25) is welded on an upper end of an outer side of the spheroidizing ladle (7) and connected to the strut head (1); an end of a positioning handle (23) is provided with a thread, the thread matches with a nut welded on the positioning shaft sleeve (25); the thread of the end of the positioning handle (23) passes through the positioning shaft sleeve (25) and fastens the strut head (1); and a position of the strut head (1) in the spheroidizing ladle (7) is adjusted by the positioning handle (23); the strut head (1) is movable and fixable at the required position; the integrated rare earth magnesium ferrosilicon nodulizer (18) coated with the rectangular steel tube or by the square steel tube is fixed beneath the strut head (1); and the bottom surface of the strut head (1) is flat; the fire-proof material coated on the strut head (1) is a frame welded by a round steel, a steel bar, and the iron wire.
 11. The method of claim 1, wherein an integrated rare earth magnesium ferrosilicon alloy (21) having a content of rare earth ≦33% and coated with a rectangular or square steel tube is arranged inside an integrated magnesium ferrosilicon nodulizer (20); a direction of an opening of the integrated magnesium ferrosilicon nodulizer (20) coated with the rectangular or square steel tube is the same as a direction of an opening of the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube; the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube is bound to a compositely coated rectangular or square steel tube (22) by welding; an alloy melt of the integrated magnesium ferrosilicon nodulizer (20) is injected into the compositely coated rectangular or square steel tube (22) to condense and cool; the cooling iron is arranged between the rectangular steel tubes or square steel tubes being filled with the alloy melt of the nodulizer; the iron melt is input into the spheroidizing ladle (7) for spheroidizing; and during a later half of the reaction time, the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube participates in the spheroidizing for supplying a required amount of rare earth.
 12. The method of claim 7, wherein an integrated rare earth magnesium ferrosilicon alloy (21) having a content of rare earth ≦33% and coated with a rectangular or square steel tube is arranged inside an integrated magnesium ferrosilicon nodulizer (20); a direction of an opening of the integrated magnesium ferrosilicon nodulizer (20) coated with the rectangular or square steel tube is the same as a direction of an opening of the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube; the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube is bound to a compositely coated rectangular or square steel tube (22) by welding; an alloy melt of the integrated magnesium ferrosilicon nodulizer (20) is injected into the compositely coated rectangular or square steel tube (22) to condense and cool; the cooling iron is arranged between the rectangular steel tubes or square steel tubes being filled with the alloy melt of the nodulizer; the iron melt is input into the spheroidizing ladle (7) for spheroidizing; and during a later half of the reaction time, the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube participates in the spheroidizing for supplying a required amount of rare earth.
 13. The method of claim 10, wherein an integrated rare earth magnesium ferrosilicon alloy (21) having a content of rare earth ≦33% and coated with a rectangular or square steel tube is arranged inside an integrated magnesium ferrosilicon nodulizer (20); a direction of an opening of the integrated magnesium ferrosilicon nodulizer (20) coated with the rectangular or square steel tube is the same as a direction of an opening of the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube; the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube is bound to a compositely coated rectangular or square steel tube (22) by welding; an alloy melt of the integrated magnesium ferrosilicon nodulizer (20) is injected into the compositely coated rectangular or square steel tube (22) to condense and cool; the cooling iron is arranged between the rectangular steel tubes or square steel tubes being filled with the alloy melt of the nodulizer; the iron melt is input into the spheroidizing ladle (7) for spheroidizing; and during a later half of the reaction time, the integrated rare earth magnesium ferrosilicon alloy (21) having the content of rare earth ≦33% and coated with the rectangular or square steel tube participates in the spheroidizing for supplying a required amount of rare earth. 